1. Field of the Invention
The present invention relates to an intake air-flow rate detecting apparatus and detecting method of an internal combustion engine.
2. Related Background Art
In the internal combustion engines, the amount of air drawn thereinto (intake air-flow rate) is detected in order to obtain optimal output and implement effective purification of exhaust gas. Generally, there are two methods to detect the intake air-flow rate. One is a method of indirectly detecting the intake air-flow rate from a vacuum inside an intake pipe by making use of correlation between intake-pipe depression and intake air-flow rate. The vacuum is detected by a sensor. Another is a method of directly detecting the intake air-flow rate by an air-flow sensor. The present invention concerns the air-flow sensor using the latter method and, more particularly, a thermal air-flow sensor.
Output of the thermal air-flow sensor involves a response lag because of structural factors of the sensor. The response lag causes little influence as long as the internal combustion engine is operating in a steady state. While the internal combustion engine is in a transient state, however, the response lag should be compensated for. A well-known system for compensating for the response lag is the one described in Japanese Patent Application Laid-Open No. H08-62012. The system described in the above application is configured to perform a first-order lag process concerning the flow rate, for the output of the thermal air-flow sensor, and thereafter linearize it to obtain the intake air-flow rate.
The system described in the above application, however, sometimes failed to attain high accuracy and there were desires for further improvement to attain higher accuracy. An object of the present invention is thus to provide an intake air-flow rate detecting apparatus and detecting method of an internal combustion engine that can compensate for the response lag of the thermal air-flow sensor with high accuracy.
An intake air-flow rate detecting apparatus of an internal combustion engine according to the present invention is characterized by comprising a thermal air-flow sensor for detecting an intake air-flow rate of the internal combustion engine; and response lag compensating means for compensating for a response lag of the air-flow sensor, using a first-order lag element concerning a heat release amount in the air-flow sensor. According to the present invention, compensating process of the response lag is carried out on the dimension of the heat release amount, whereby the response lag of the air-flow sensor can be compensated for with accuracy. Since the response lag in the air-flow sensor is caused mainly by the phenomenon of heat balance at a detector part, the compensating process on the dimension of heat release amount is fitter for the actual phenomenon and can improve the accuracy.
It is preferable herein that the response lag compensating means be configured to divide the air-flow sensor into a plurality of sections, take account of first-order lag elements concerning heat release amounts in the respective sections, and combine them, thereby compensating for the response lag of the whole of the air-flow sensor. The accuracy is enhanced by carrying out the compensating processes of the first-order response lags concerning the heat release amounts in the respective sections and combining them. Particularly, it is preferable that the detector part of said air-flow sensor be divided into a bobbin section, a lead wire, and a support section and that first-order response lags of the respective sections be taken into account.
Further, it is preferable that said response lag compensating means determine each of time constants of first-order lag models for the respective sections, based on the intake air-flow rate (the word xe2x80x9cair-flow ratexe2x80x9d includes the meanings of xe2x80x9cflow ratexe2x80x9d and xe2x80x9cflow amountxe2x80x9d in this application) detected by said air-flow sensor. For compensating for the response lag, the compensation is made as first-order lag behavior concerning the heat release amounts and the time constants of such first-order lag systems are determined based on the flow amount or the flow rate, whereby the accuracy can be enhanced further more. Particularly, it is preferable that the time constants be determined based on a flow amount per unit cross section of an intake passage on which the air-flow sensor is disposed. When the time constants are determined based on the flow amount per unit cross section, there is no need for execution of experiment for matching among internal combustion engines with different cross sections of the intake passage. And also a map of relation between the output voltage of the air-flow sensor and the time constant can be mounted on the apparatus.
An intake air-flow rate detecting method of an internal combustion engine according to the present invention is a method wherein, using a first-order lag element concerning a heat release amount in a thermal air-flow sensor for detecting an intake air-flow rate of the internal combustion engine, a response lag of said air-flow sensor is compensated for. According to the present invention, the compensating process of the response lag is carried out on the dimension of the heat release amount, whereby the response lag of the air-flow sensor can be compensated for with accuracy. Since the response lag in the air-flow sensor is caused mainly by the phenomenon of heat balance at the detector part, the process on the dimension of heat release amount is fitter for the actual phenomenon and can improve the accuracy.
It is preferable here that the response lag of the whole of said air-flow sensor be compensated for by dividing said air-flow sensor into a plurality of sections, taking account of first-order lag elements concerning heat release amounts in the respective sections, and combining the first-order lag elements of the respective sections. The accuracy is enhanced by carrying out the compensating processes of the first-order response lags concerning the heat release amounts in the respective sections and combining them. Particularly, it is preferable that the detector part of said air-flow sensor be divided into a bobbin section, a lead wire, and a support section and that first-order response lags of the respective sections be taken into account.
Further, it is preferable that each of time constants of first-order lag models for the respective sections be determined based on a flow rate or a flow amount of the intake air-flow rate detected by said air-flow sensor. For compensating for the response lag, the compensation is made as the first-order lag behavior concerning the heat release amounts and the time constants of such first-order lag systems are determined based on the flow amount or the flow rate, whereby the accuracy can be enhanced further more.
Particularly, it is preferable that the time constants be determined based on a flow amount per unit cross section of an intake passage on which the air-flow sensor is disposed. When the time constants are determined based on the flow amount per unit cross section, there is no need for execution of experiment for matching among internal combustion engines with different cross sections of the intake passage. And also a map of relation between the output voltage of the air-flow sensor and the time constant can be mounted on the apparatus.
The present invention will become more fully understood from the detailed description given hereinbelow and the accompanying drawings which are given by way of illustration only, and thus are not to be considered as limiting the present invention.
Further scope of applicability of the present invention will become apparent from the detailed description given hereinafter. However, it should be understood that the detailed description and specific examples, while indicating preferred embodiments of the invention, are given by way of illustration only, since various changes and modifications within the spirit and scope of the invention will become apparent to those skilled in the art from this detailed description.